ARLINGTON, VA., August 18, 1863.

Lieutenant Colonel THOS. ALLCOCK,

Commanding Fort Ethan Allen:

The following telegram has just been received, and is respectfully forwarded for your information:

WASHINGTON, August 18, 1863.

General G. A. DE RUSSY:

Colonel Lowell, Second Massachusetts Cavalry, has moved with his entire available force toward Leesburg, where White is reported to be with the main body of his people.

J. H. TAYLOR,

Chief of Staff, and Assistant Adjutant-General.

Respectfully,

G. A. DE RUSSY.

CENTREVILLE, VA., August 18, 1863-4 p. m.

(Received 4. 20 p. m.)

Colonel J. H. TAYLOR,

Chief of Staff:

The following dispatch has just been received from Manassas. Not knowing whether the information has been communicated to headquarters in Washington, I send it to you. I have directed a small party of cavalry to proceed at once to Gainesville and Hay Market, to ascertain, if possible, what truth there is in the report:

MANASSAS JUNCTION, VA., August 18, 1863.

Brigadier-General KING:

General Williams telegraphed me last evening that 4,000 cavalry had come down from the Shenandoah Valley, and were making their way around our rear through Hopewell and Hay Market. They were said to be at Salem yesterday morning. My regiment has been under arms since then, and a whole division of the Eleventh Corps has just come down here, and just above, a battery of artillery. My idea is they will endeavor to get around you and go to Fairfax Station, or try to cut the railroad. Can you spare me any cavalry? I have not a single hoof. Our pickets extend out 2 1/2 miles on the road to Centreville, and half as far on the railroad toward Union Mills. Will be happy to co-operate with you.

ALFRED GIBBS,

Colonel, Commanding 130th New York Volunteers.

REFUS KING,

Brigadier-General.

CLARKSBURG, W. VA., August 18, 1863.

(Received 11. 20 p. m.)

Brigadier-General CULLUM:

I came up from Harper's Ferry and New Creek last night. All quiet along line of railroad. General Averell is at Petersburg, in Hardy County,and will move to-morrow on his expedition into Pendleton, Highland, Pocahontas, Bath,and Greenbrier Counties. Will destroy the saltpeter and powder works in Pendleton as he goes through. General Scammon reports all quiet in the Kanawha Valley.